Flexible sealed pouches are currently used in many packaging applications. By way of example only, pouches are used to package individual servings of granular materials such as sugar, sweeteners, powders for beverages such as hot chocolate, liquid condiments such as mayonnaise, ketchup, mustard or the like, and other food stuffs or consumer goods.
In one form of pouch packaging, a web of pouch material is fed from a supply roll. The web is folded longitudinally and transverse seals are formed to provide a train of serially disposed pouches, open along a top edge and connected side-by-side by virtue of the seals. The pouches are separated from each other by cutting the train transversely along the seal locations, and are then transported about a filler wheel for filling and top end sealing.
It is desirable to separate or cut the pouches one from the other in a manner to provide uniform sized pouches. Stated in another way, it is desirable to form pouches having side seals of equal width relative to other pouches.
In order to fulfill this goal, it is desirable to cut the pouches in the center of the transverse seals with an equal width of the seal disposed on each side of the cut, and on each pouch side. It is thus necessary to provide a means by which the cutter or knife is operated in a manner so as to produce such cuts repeatably in the seal center for all pouch line speeds utilized.
One method of accomplishing this would be to mark or "register" the web to indicate the center of each seal, sense the mark or register, and drive the cutter in response to such sensing after any system delay.
Such methods have certain inherent disadvantages. For example, the register sensing method requires an indexed or registered web, and a means for sensing the web.
Accordingly, it has been one objective of the invention to provide improved apparatus and methods for sensing the location of transverse seals across a multiple ply or moving web.
It has been another objective of the invention to provide improved apparatus and methods for separating pouches from a train of interconnected pouches.
Another objective of the invention has been to provide improved methods and apparatus for detecting seal areas between pouches in an unregistered, non-indexed train of pouches.
Another objective of the invention has been to provide an improved seal sensing and control system for consistently establishing a cut within sensed transverse areas of a multiple ply web and within a fine tolerance range.
To these ends, a preferred embodiment of the invention comprises running a two-ply intermittently sealed web through a gap between two opposed ports, each connected to a vacuum. As the unsealed web portions are drawn across the ports, they are pulled apart and against the respective ports. This seals the ports to establish a non-zero or static pressure on the vacuum sides of the port. When the seal area moves through the gap, the vacuum at each port tries to pull the web toward the respective ports. Due to the seal, however, the material can be pulled only to one side or the other. When this pulling occurs, the sealed laminate remains stuck to one side or the other. The opposite port is opened, breaking the vacuum. This port opening causes a pressure change which is sensed to signal the introduction of the seal area to the gap between aligned, opposed vacuum ports. As the web continues, the seal passes the vacuum ports and the web material again is pulled out to cover each vacuum port. This reestablishes a threshold pressure in the system which event can be sensed to indicate seal passage. Seal position and width is thus sensed for the pouch line speed. These sensing signals are utilized to drive a controller for operating a downstream cutter on a delay sufficient to divide or separate the pouches down the middle of the seal area. Moreover, in order to maintain the cuts at the center of each seal area within desirable tolerances, a central loop is used for comparison and correction. This comprises an encoder driven from the master filler wheel axis or servo, with encoder counts divided by a predetermined pouch pitch or length setting (in the longitudinal web flow direction). This encode signal is compared in a programmable logic controller to the seal sensing signal frequency to establish an error and the system is operable to repeatedly collapse that error at a slew rate controller to avoid over correction. A slaved axis or servo for the web drive feeding the cutter is thus controlled as a function of web speed, predetermined pouch pitch, sensed seals and a comparatively generated error to maintain the seal position relative to the cutter within an acceptable tolerance range for the application.
It will be appreciated that the invention has many uses or applications for both intermittent and continuous motion machines, not only for pouches but in many applications where intermittent seals must be accurately sensed. No web register is required, nor are any change parts required due to varied web line speeds and web materials.